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rwsem.h

#ifndef _S390_RWSEM_H
#define _S390_RWSEM_H

/*
 *  include/asm-s390/rwsem.h
 *
 *  S390 version
 *    Copyright (C) 2002 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
 *
 *  Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
 */

/*
 *
 * The MSW of the count is the negated number of active writers and waiting
 * lockers, and the LSW is the total number of active locks
 *
 * The lock count is initialized to 0 (no active and no waiting lockers).
 *
 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
 * uncontended lock. This can be determined because XADD returns the old value.
 * Readers increment by 1 and see a positive value when uncontended, negative
 * if there are writers (and maybe) readers waiting (in which case it goes to
 * sleep).
 *
 * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
 * be extended to 65534 by manually checking the whole MSW rather than relying
 * on the S flag.
 *
 * The value of ACTIVE_BIAS supports up to 65535 active processes.
 *
 * This should be totally fair - if anything is waiting, a process that wants a
 * lock will go to the back of the queue. When the currently active lock is
 * released, if there's a writer at the front of the queue, then that and only
 * that will be woken up; if there's a bunch of consequtive readers at the
 * front, then they'll all be woken up, but no other readers will be.
 */

#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif

#ifdef __KERNEL__

#include <linux/list.h>
#include <linux/spinlock.h>

struct rwsem_waiter;

extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_write(struct rw_semaphore *);

/*
 * the semaphore definition
 */
struct rw_semaphore {
      signed long       count;
      spinlock_t        wait_lock;
      struct list_head  wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
      struct lockdep_map      dep_map;
#endif
};

#ifndef __s390x__
#define RWSEM_UNLOCKED_VALUE  0x00000000
#define RWSEM_ACTIVE_BIAS     0x00000001
#define RWSEM_ACTIVE_MASK     0x0000ffff
#define RWSEM_WAITING_BIAS    (-0x00010000)
#else /* __s390x__ */
#define RWSEM_UNLOCKED_VALUE  0x0000000000000000L
#define RWSEM_ACTIVE_BIAS     0x0000000000000001L
#define RWSEM_ACTIVE_MASK     0x00000000ffffffffL
#define RWSEM_WAITING_BIAS    (-0x0000000100000000L)
#endif /* __s390x__ */
#define RWSEM_ACTIVE_READ_BIAS      RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS     (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

/*
 * initialisation
 */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif

#define __RWSEM_INITIALIZER(name) \
 { RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait.lock), \
   LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }

#define DECLARE_RWSEM(name) \
      struct rw_semaphore name = __RWSEM_INITIALIZER(name)

static inline void init_rwsem(struct rw_semaphore *sem)
{
      sem->count = RWSEM_UNLOCKED_VALUE;
      spin_lock_init(&sem->wait_lock);
      INIT_LIST_HEAD(&sem->wait_list);
}

extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
                   struct lock_class_key *key);

#define init_rwsem(sem)                   \
do {                                \
      static struct lock_class_key __key; \
                                    \
      __init_rwsem((sem), #sem, &__key);  \
} while (0)


/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
      signed long old, new;

      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     ahi   %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     aghi  %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count),
              "i" (RWSEM_ACTIVE_READ_BIAS) : "cc", "memory");
      if (old < 0)
            rwsem_down_read_failed(sem);
}

/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
      signed long old, new;

      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   ltr   %1,%0\n"
            "     jm    1f\n"
            "     ahi   %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b\n"
            "1:"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   ltgr  %1,%0\n"
            "     jm    1f\n"
            "     aghi  %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b\n"
            "1:"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count),
              "i" (RWSEM_ACTIVE_READ_BIAS) : "cc", "memory");
      return old >= 0 ? 1 : 0;
}

/*
 * lock for writing
 */
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
      signed long old, new, tmp;

      tmp = RWSEM_ACTIVE_WRITE_BIAS;
      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     a     %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     ag    %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count), "m" (tmp)
            : "cc", "memory");
      if (old != 0)
            rwsem_down_write_failed(sem);
}

static inline void __down_write(struct rw_semaphore *sem)
{
      __down_write_nested(sem, 0);
}

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
      signed long old;

      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%2)\n"
            "0:   ltr   %0,%0\n"
            "     jnz   1f\n"
            "     cs    %0,%4,0(%2)\n"
            "     jl    0b\n"
#else /* __s390x__ */
            "     lg    %0,0(%2)\n"
            "0:   ltgr  %0,%0\n"
            "     jnz   1f\n"
            "     csg   %0,%4,0(%2)\n"
            "     jl    0b\n"
#endif /* __s390x__ */
            "1:"
            : "=&d" (old), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count),
              "d" (RWSEM_ACTIVE_WRITE_BIAS) : "cc", "memory");
      return (old == RWSEM_UNLOCKED_VALUE) ? 1 : 0;
}

/*
 * unlock after reading
 */
static inline void __up_read(struct rw_semaphore *sem)
{
      signed long old, new;

      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     ahi   %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     aghi  %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count),
              "i" (-RWSEM_ACTIVE_READ_BIAS)
            : "cc", "memory");
      if (new < 0)
            if ((new & RWSEM_ACTIVE_MASK) == 0)
                  rwsem_wake(sem);
}

/*
 * unlock after writing
 */
static inline void __up_write(struct rw_semaphore *sem)
{
      signed long old, new, tmp;

      tmp = -RWSEM_ACTIVE_WRITE_BIAS;
      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     a     %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     ag    %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count), "m" (tmp)
            : "cc", "memory");
      if (new < 0)
            if ((new & RWSEM_ACTIVE_MASK) == 0)
                  rwsem_wake(sem);
}

/*
 * downgrade write lock to read lock
 */
static inline void __downgrade_write(struct rw_semaphore *sem)
{
      signed long old, new, tmp;

      tmp = -RWSEM_WAITING_BIAS;
      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     a     %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     ag    %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count), "m" (tmp)
            : "cc", "memory");
      if (new > 1)
            rwsem_downgrade_wake(sem);
}

/*
 * implement atomic add functionality
 */
static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
{
      signed long old, new;

      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     ar    %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     agr   %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count), "d" (delta)
            : "cc", "memory");
}

/*
 * implement exchange and add functionality
 */
static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
{
      signed long old, new;

      asm volatile(
#ifndef __s390x__
            "     l     %0,0(%3)\n"
            "0:   lr    %1,%0\n"
            "     ar    %1,%5\n"
            "     cs    %0,%1,0(%3)\n"
            "     jl    0b"
#else /* __s390x__ */
            "     lg    %0,0(%3)\n"
            "0:   lgr   %1,%0\n"
            "     agr   %1,%5\n"
            "     csg   %0,%1,0(%3)\n"
            "     jl    0b"
#endif /* __s390x__ */
            : "=&d" (old), "=&d" (new), "=m" (sem->count)
            : "a" (&sem->count), "m" (sem->count), "d" (delta)
            : "cc", "memory");
      return new;
}

static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
      return (sem->count != 0);
}

#endif /* __KERNEL__ */
#endif /* _S390_RWSEM_H */

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